The present invention generally relates to a film-forming apparatus, and more particularly, to a technical field of chemical vapor deposition (CVD).
Currently, gallium nitride (GaN) is used as a material of electronic elements such as a light-emitting diode (LED). In order to manufacture crystals of gallium nitride, a film-forming apparatus of a metalorganic chemical vapor deposition (MOCVD) method is used.
FIG. 7 shows an internal configuration diagram illustrating a conventional film-forming apparatus 110 of a MOCVD method.
The film-forming apparatus 110 includes a vacuum chamber 111, a plurality of feedstock gas pipes 127a for introducing a feedstock gas into the inner side of the vacuum chamber 111, a plurality of reactive gas pipes 127b for introducing a reactive gas into the inside of the vacuum chamber 111, and a heating device 143 for heating the object to be film-formed 140 located in the inner side of the vacuum chamber 111. Reference numeral 113 denotes a vacuum evacuator for vacuum evacuating the inside of the vacuum chamber 111.
A substrate holder 141 that holds the object to be film-formed 140 on its surface (holding surface) is provided inside the vacuum chamber 111. Reference numeral 147 denotes a rotator for rotating the substrate holder 141.
The heating device 143 includes an electrothermal resistor 142 and a power supply 144. The electrothermal resistor 142 is installed in the substrate holder 141; and the power supply 144 is electrically connected to the electrothermal resistor 142.
A cooling chamber 121 is arranged in a position facing the holding surface of the substrate holder 141. The cooling chamber 121 is connected to a cooling medium supply unit 155 for supplying a cooling medium to the inner side of the cooling chamber and a cooling medium discharge unit 156 for discharging the cooling medium to the outer side.
A reactive gas chamber 126 is arranged in a position opposite to the substrate holder 141 of the cooling chamber 121; and a feedstock gas chamber 134 is arranged in a position opposite to the cooling chamber 121 of the reactive gas chamber 126.
The feedstock gas introduction pipe 127a is arranged to penetrate the reactive gas chamber 126 and the cooling chamber 121. One end of the feedstock gas introduction pipe 127a is connected to the inner side of the feedstock gas chamber 134; and the opening 128a of the other end is exposed inside the vacuum chamber 111. The reactive gas introduction pipe 127b is arranged to penetrate the cooling chamber 121. One end of the reactive gas introduction pipe 127b is connected to the inner side of the reactive gas chamber 126; and the opening 128b of the other end is exposed inside the vacuum chamber 111.
The feedstock gas tank 151 arranged outside the vacuum chamber 111 is connected to the feedstock gas chamber 134; and the reactive gas tank 152 is connected to the reactive gas chamber 135. As the feedstock gas and the reactive gas are supplied to the inner sides of the feedstock gas chamber 134 and the reactive gas chamber 126 from the feedstock gas tank 151 and the reactive gas tank 152, respectively, the feedstock gas and the reactive gas are discharged to the inner side of the vacuum chamber 111 through the feedstock gas introduction pipe 127a and the reactive gas introduction pipe 127b, respectively. The feedstock gas and the reactive gas supplied from the feedstock gas tank 151 and the reactive gas tank 152, respectively, are not mixed until they are discharged to the inner side of the vacuum chamber 111.
When an electric current flows from the power supply 144 to the electrothermal resistor 142, and the object to be film-formed 140 on the substrate holder 141 is heated, a thin film is formed on the surface of the object to be film-formed 140 inside the vacuum chamber 111 by virtue of a chemical reaction between the discharged feedstock gas and the discharged reactive gas.
In order to mix the feedstock gas and the reactive gas immediately before the surface of the object to be film-formed 140, the opening 128a of the end portion of the feedstock gas introduction pipe 127a and the opening 128b of the end portion of the reactive gas introduction pipe 127b are located near the surface of the object to be film-formed 140. If the object to be film-formed 140 is heated to a high temperature, the feedstock gas introduction pipe 127a and the reactive gas introduction pipe 127b are heated by the heat of the object to be film-formed 140, so that the feedstock gas and the reactive gas may be decomposed inside each pipe 127a and 127b. In particular, when the feedstock gas is an organic metal gas, it is highly probable that the feedstock gas becomes thermally decomposed inside the feedstock gas introduction pipe 127a. 
Accordingly, it is necessary to cool the feedstock gas introduction pipe 127a and the reactive gas introduction pipe 127b using the thermal transfer with the cooling medium by flowing the temperature-controlled cooling medium from the cooling medium supply unit 155 through the inner side of the cooling chamber 121 and discharging the cooling medium from the cooling medium discharge unit 156 during the film formation.
However, in the film-forming apparatus 110 of the conventional art, both the feedstock gas introduction pipe 127a and the reactive gas introduction pipe 127b are arranged to penetrate the same cooling chamber 121. Therefore, if the cooling medium flows through the inner side of the cooling chamber 121, the cooling medium may diffuse to the inner side of the cooling chamber 121 so as to generate whirling or partial clogging of the flow, thereby resulting in a temperature of the cooling medium inside the cooling chamber 121 or a cooling effect of each pipe 127a and 127b becoming non-uniform.
For example, when the center of the object to be film-formed 140 is easily heated in comparison to the outer edge, the pipes 127a and 127b arranged to face the center of the object to be film-formed 140 are heated to a temperature higher than the temperature of the other pipes, even when the cooling medium flows through the inner side of the cooling chamber 121; and consequently, the feedstock gas or the reactive gas inside the pipe 127a or 127b may be thermally decomposed. Furthermore, because a temperature distribution is not uniform between the center and the outer edge of the object to be film-formed 140, there is a problem in that the quality of the formed thin film may become non-uniform (Japanese Patent No. 3442536).